Eric Hovde is challenging Tommy Thompson in Wisconsin Senate primary

In 2010, Johnson, the owner and CEO of a plastics manufacturing company in Oshkosh, burst out of nowhere and into the U.S. Senate. With a self-funded campaign, Johnson swamped two little-known Republicans in the primary, garnering 85% of the vote. He then went on to unseat three-term Democratic Sen. Russ Feingold, 52% to 47%.

Now some see Hovde, 47, the scion of a Madison real estate developer and a wealthy hedge fund manager in his own right, poised to execute a similar coup.

If he does, it would represent a stunning upset in the Republican camp. Two months ago, former Wisconsin Gov. Tommy Thompson seemed almost a sure bet to win the GOP nod to run for the seat that Herb Kohl is vacating at the end of this year.

Thompson's campaign pointed to polls that showed him not only well ahead of his three GOP rivals - Hovde, former 1st District Congressman Mark Neumann, and Assembly Speaker Jeff Fitzgerald - but also the only one with a lead over the one Democrat seeking the seat, U.S. Rep. Tammy Baldwin of Madison.

Lately, though, Thompson's victory in the Republican primary on Aug. 14 no longer seems so certain.

New polls show Hovde, who only recently returned to the Badger State after a quarter century away, at least gaining on Thompson in the primary. In the July installment of Public Policy Polling, a national polling firm, gave Hovde a one-point lead over Thompson and suggested Hovde would do marginally better against Baldwin than Thompson would.

In its newest poll out this week, PPP put Hovde still in the lead, with 28% - but also reported a new surge by Neumann, now tied with Thompson at 25%. "Hovde remains the unexpected leader in this contest but his momentum has stalled," the polling firm says.

Yard signs and larger highway placards for Hoved are blossoming around the state.

"Conservative distrust of both Neumann and Thompson gave Hovde an opening that he took advantage of," says James Wigderson, a Waukesha-based political blogger and contributor to the MacIver Institute, a conservative news and commentary website. "I think he's within striking distance of Thompson, although I would still put Thompson as the favorite."

It's not just Hovde's ability to fund much of his own campaign that has helped propel the political neophyte into the top tier - it's how he's spent the money. This spring, as the recall elections were soaking up attention, airtime and political donations, Hovde invested in a series of positive TV spots to get his name before voters while his rivals sat on the sidelines. That clearly has helped him.

"Hovde advertising earlier than the others allowed him to build name recognition and establish himself before the other candidates defined him," says Wigderson.

The investment only went so far, however. In July's polling, says Franklin, the Marquette Law survey found that the number of primary voters who said they didn't know enough about Hovde to have an opinion on him was still more than 50%.

What does Hovde stand for? Isthmus has been seeking an interview with him since June to no avail. While an aide to the candidate expressed willingness to arrange one, the campaign has repeatedly deferred the request, saying Hovde's schedule was too crowded to take the time for it.

On his website, Hovde joins virtually all other state and national GOP candidates in vowing to "repeal and replace" the Patient Protection and Affordable Care Act, a.k.a. "Obamacare." He instead promotes "private-sector solutions" to address rising health care costs and providing care for the uninsured.

He also vows to shrink government and the federal deficit; eliminate most "tax loopholes" (but not the tax deduction for contributions to charity or the mortgage interest deduction) and thereby sharply reduce the size and reach of the Internal Revenue Service; cut the number of tax brackets to just two (10% and 25%); and reduce regulation.

Hovde embraces an anti-Wall Street populist rhetoric, vowing to end "bailouts" and to seek the repeal of the Dodd-Frank financial industry regulation law; this even while banks in which his business invested took some $9 million in funds under the Troubled Asset Relief Program.

Hovde has yet to release his own tax returns (following the example of presumptive GOP presidential nominee Mitt Romney, who to date has released only one year's returns and an estimate for 2011). But revelations in the Milwaukee Journal Sentinel that Hovde's net worth exceeds $50 million and includes holdings in the Cayman Islands - where money vacations to escape taxes - led the state Democratic Party to hammer him with press releases asking "what is Eric Hovde hiding?"

The Democrats also noted that his candidate's financial disclosure forms "do not answer questions about how or whether Hovde has taken advantage of government subsidies and tax loopholes at the expense of middle-class taxpayers."

Hovde has drawn some flak for unvarnished comments that quickly went viral, including his complaint that reporters are too enamored of "sob stories" about food-stamp recipients while ignoring the plight of business people. He said his comments were taken out of context. Hovde was also accused of red-baiting when he told The Hill, a Washington political newspaper, that Baldwin's "philosophy has its roots in Marxism, communism, socialism, extreme liberalism...." Such remarks don't seem to have hurt him with the GOP base.

Thompson and Neumann have both taken aim at the upstart candidate in their advertising - forgetting Ronald Reagan's famous 11th Commandment not to speak ill of a fellow Republican.

"The Washington game - Eric Hovde's been playing it for 24 years," intones a Thompson TV ad launched in late July. Moving a game piece with Hovde's picture on it around a Monopoly-like board, the ad charges that Hovde and his Washington-based fund "used Uncle Sam to buy banks...traded on government contacts to profit from taxpayer bailouts...bet against American companies," and bragged about foreclosing on strapped homeowners in the fiscal crisis.

The sharp criticism by Hovde's well-known rivals has done some damage; PPP notes that 30% of its sample now view him negatively, up from 9% last month. And in the end, Thompson could win if the anti-Thompson vote splits between Hovde and Neumann.

But the very complexity of that calculus points to perhaps the biggest difference between Hovde and the man whose success he would like to emulate, Ron Johnson.

Their similarity - "being a political novice businessperson coming out of nowhere," as Franklin puts it - is overshadowed by their very different competitive contexts. "Ron Johnson wasn't facing Mark Neumann or Tommy Thompson," Franklin says. "Johnson had an infinitely easier primary."

But don't count Hovde out yet, says Wigderson. He notes Thompson's most commonly cited talking point - that only he can beat Baldwin - may not be enough to rally the enthusiasm he needs to win the primary. It also may not be accurate.

"I think people may be underestimating Hovde," he says. "This is not a guy who needs coaching on the issues. His conservatism is sincere. He can match Baldwin dollar for dollar. He's a hard campaigner. I think he can win."